Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 10, 1513-1522, 2010
https://doi.org/10.5194/nhess-10-1513-2010
© Author(s) 2010. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
12 Jul 2010
Application of polarization ellipse technique for analysis of ULF magnetic fields from two distant stations in Koyna-Warna seismoactive region, West India
F. Dudkin1, Gautam Rawat2, B. R. Arora2, V. Korepanov1, O. Leontyeva1,*, and A. K. Sharma3 1Lviv Centre of Institute of Space Research, Lviv, 79000, Ukraine
2Wadia Institute of Himalayan Geology, Dehradun, 248 001, India
3Department of Physics, Shivaji University, Kolhapur, India
*Invited contribution by O. Leontyeva, recipient of the EGU Young Scientists Outstanding Poster Paper Award 2008.
Abstract. A new approach is developed to find the source azimuth of the ultra low frequency (ULF) electromagnetic (EM) signals believed to be emanating from well defined seismic zone. The method is test applied on magnetic data procured from the seismoactive region of Koyna-Warna, known for prolonged reservoir triggered seismicity. Extremely low-noise, high-sensitivity LEMI-30 search coil magnetometers were used to measure simultaneously the vector magnetic field in the frequency range 0.001–32 Hz at two stations, the one located within and another ~100 km away from the seismic active zone. During the observation campaign extending from 15 March to 30 June 2006 two earthquakes (EQs) of magnitude (ML>4) occurred, which are searched for the presence of precursory EM signals.

Comparison of polarization ellipses (PE) parameters formed by the magnetic field components at the measurement stations, in select frequency bands, allows discrimination of seismo-EM signals from the natural background ULF signals of magnetospheric/ionospheric origin. The magnetic field components corresponding to spectral bands dominated by seismo-EM fields define the PE plane which at any instant contains the source of the EM fields. Intersection lines of such defined PE planes for distant observation stations clutter in to the source region. Approximating the magnetic-dipole configuration for the source, the magnetic field components along the intersection lines suggest that azimuth of the EM source align in the NNW-SSE direction. This direction well coincides with the orientation of nodal plane of normal fault plane mechanism for the two largest EQs recorded during the campaign. More significantly the correspondence of this direction with the tectonic controlled trend in local seismicity, it has been surmised that high pressure fluid flow along the fault that facilitate EQs in the region may also be the source mechanism for EM fields by electrokinetic effect.


Citation: Dudkin, F., Gautam Rawat, Arora, B. R., Korepanov, V., Leontyeva, O., and Sharma, A. K.: Application of polarization ellipse technique for analysis of ULF magnetic fields from two distant stations in Koyna-Warna seismoactive region, West India, Nat. Hazards Earth Syst. Sci., 10, 1513-1522, https://doi.org/10.5194/nhess-10-1513-2010, 2010.
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